A conventional wall-mounted load control device is mounted to a standard electrical wall box and is connected in series electrical connection with a load. Standard load control devices, such as dimmers and fan speed controls, use one or more semiconductor switches, such as triacs or field effect transistors (FETs), to control the current delivered to the load, and thus, the intensity of the lighting load or the speed of the motor.
Wall-mounted load control devices typically include a user interface having a means for adjusting the intensity or the speed of the load, such as a linear slider, a rotary knob, or a rocker switch. Some load control devices also include a button that allows for toggling of the load from off (i.e., no power is conducted to the load) to on (i.e., power is conducted to the load). It is often desirable to include a plurality of status indicators, such as light emitting diodes (LEDs), on the user interface to indicate the intensity or speed of the load.
FIG. 1 shows the user interface of a prior art dimmer 10 having a plurality of status indicators 20. As shown, the dimmer 10 includes a faceplate 30, a bezel 35, an intensity selection actuator 40 for selecting a desired level of light intensity of an associated lighting load controlled by the dimmer, and a control switch actuator 50. Pressing the actuator 50 may cause the associated lighting load to toggle from on to off, or vice versa. Actuation of the upper portion of actuator 40 increases or raises the light intensity of the lighting load, while actuation of the lower portion of actuator 40 decreases or lowers the light intensity. The intensity levels of the lighting load may range from a minimum intensity level, which is preferably the lowest visible intensity, but which may be zero, or “full off,” to a maximum intensity level, which is typically “full on.” Light intensity level is typically expressed as a percent of full intensity. Thus, when the lighting load is on, light intensity level may range from 1% to 100%.
The dimmer 10 also includes an intensity level indicator in the form of the plurality of status indicators 20. The status indicators 20 may be arranged in an array (such as a linear array as shown) representative of a range of light intensity levels of the lighting load being controlled. The status indicators 20 operate to indicate the intensity of the associated lighting load by illuminating a percentage of the individual status indicators equivalent to the dimming level (i.e., the percentage of full intensity). For example, if the dimmer 10 is controlling the lighting load to 50%, the middle status indicator will be illuminated, since this status indicator is at the midpoint of the linear array of the status indicators 20.
Since it is common to include a lighting load in the same enclosure as a fan motor, load control devices that include both a dimmer circuit and a fan speed control circuit in a single wall-mountable device to provide independent control of the lighting load and the fan motor have been developed. Prior art dual light/fan control devices have not included rocker switches or status indicators (as the dimmer 10 of FIG. 1), but have included two side-by-side sliders, the positions of which have inherently provided visual feedback of the lighting level and the fan speed level. One example of a dual light/fan speed control is the SKYLARK Dual Slide-to-off Fan Speed Control and Dimmer, model number S2-LFSQ, manufactured by Lutron Electronics Co., Inc.
It is desirable to provide illuminated status indicators on the user interface of a dual light/fan speed control that are independent of any actuators in order to provide feedback of both the controlled light level and the fan speed to the end user. While the feedback provided by the status indicators 20 of the prior art dimmer 10 approximates the light level of the controlled load, a second means of visual feedback is provided to the user of the dimmer through observation of changes in the intensity of the physical lighting load. However, when a fan motor is controlled by a load control device, the mechanical inertia of the fan motor is so great that an immediate visual feedback of the speed of the fan motor by observation of the fan is not possible. Thus, there is a need to provide immediate visual feedback of the speed of the fan motor on the status indicators, so that the user will know to what speed the fan motor is being controlled.
Most prior art quiet fan speed controls have only allowed a user to control the fan speed to one of a select number of discrete speeds, which is often only three speeds. However, it is desirable to offer a greater number of discrete fan speeds that are selectable from the user interface of a fan speed control. If the number of discrete fan speeds is greater than the number of status indicators provided on the user interface, it is not possible to display the fan speeds, as a percentage of the maximum fan speed (as the dimmer 10 displays the intensity of the lighting load), using only a single active or illuminated stats indicator for each discrete speed.
Thus, there exists a need for a fan speed control that offers a discrete number of fan speeds M that is greater than the number of status indicators N on the user interface. There is also a need for a method for illuminating the status indicators to provide a unique indication of each discrete fan speed so that an end user can easily and immediately determine the present status of the fan speed control.